Flow regime wetted area

It is the full wetted perimeter that determines the flow regime and the velocity gradients in a channel. So, in this book, de determined using the full wetted perimeter will be used for both pressure drop and heat transfer calculations. The actual area through which the heat is transferred should, of course, be used to determine the rate of heat transfer equation 12.1. 

In the trickle-flow regime, only part of the catalyst surface is covered by a film of liquid, and it is sometimes assumed that only this part of the catalyst is effective. Correlations for the fraction wetted area, have been used... 

The periodic liquid flow changes the hydrodynamic regime and influences the external and internal catalyst wetting. Therefore the catalyst particle wetted area will be increased and decreased depending on the hquid duration. The degree of wetting will be crucially influenced. This has a strong effect on the intensity of the process, as it alters the conditions of transport of the reactants to the catalyst surface where adsorption, chemical reactions and desorption of the products take place. 

Berner and Kalis [245] proceed from the expressions for the film thickness in laminar and turbulent regime and the assumption fm- complete wetting, or a constant wetted area independent of the liquid flow rate, and obtained the equations ... 

Mass transfer correlations from liquid to solids are based on total interfacial area of the solids. Hence, the correlations include partial wetting effects. As expected, the mass transfer coefficient increases with Increasing liquid flow rate. It is somewhat insensitive to the gas flow rate. The sensitivity to the gas rate increases in the pulse and dispersed bubble regime. 

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